Twisted Pair Cables — How Twisted?

[joegib]

Hi,

I won't bore you with a long backstory but for various reasons I need to replace the telephone cable between my NTE5 socket and the IDC-type junction box connected to the drop cable where it enters my flat. Basically, therefore, I need to obtain a length (say 10 metres) of decent quality 4-core, twin-pair CW1308 cable. (Decent enough quality, that is, so that an Openreach engineer won't raise his eyebrows if he inspects the setup). My problem is reliably obtaining cable of the right quality/spec.

Several years ago I planned running an extension line from the NTE5 socket and bought a length of allegedly CW1308 cable from Maplins. On examination, this struck me as very poor stuff. The internal wires ran loosely in an outer covering that was more like a PVC tube than the kind of tight sheath covering I'd seen on other kinds of cable I'd handled. Stripping an 18 inch length showed the wires bunched in a very slow spiral (but that might have been an optical illusion!). The blue and orange pairs were certainly not organised in separate twisted pairs. This looked nothing like the cable pictured here for instance (ignoring the additional pairs):

http://www.hyperline.com/img/sharedimg/cable/cable1-2.jpg

So, to come to the point, if I order CW1308 4-core cable what should it look like, please, so that I can satisfy myself that it's genuine twisted pair.

Thanks for any help.

Joe

 

[Lectrician]

CW1308 is not tightly twisted. Do not compare it to Cat5e.

The sheath on 'proffesional' cable is VERY loosly fitting, but holds a true 'cylindrical' shape.

The cheap crap has a thin PVC sheath which is tight, hard to remove, and takes the shape of the internal cores.

The open openreach stuff is also a touch 'off white'.

You are never going to match their cable exactly. You may find cable of equal quality. You need to just look. Each wholesaler & merchant stocks different stuff.

Can you not move the NTE to the position of the joint box you mention, and then fit extension wiring as required?

 

[joegib]

Thanks for the reply.

Unfortunately, your suggestion can't be applied in my situation. There's only about a foot length of drop cable between its entry point by my front door and its connection to the IDC junction box. The IDC box is is located on the narrow frame between the top of the door and the fanlight. The NTE5 socket just couldn't be fitted there without obstructing the door.

Still, your description of CW1308 cable shows that my ideas about what it "should" look like are wrong. As you say, I'll need to keep looking. I've ordered a length off an Ebay trader I've had reliable dealings with so I'll see how I get on.

Thanks again.

Joe

 

[simonpolly]

Just as a matter of interest what is wrong with the cable that is already there ?,i can tell you that 10 mtrs of cat5 quality will make no difference over 10 mtrs of ordinary bt internal cable as long as the internal cable has not faults.

 

[joegib]

I'm sure you're right but the problem was that the existing cable between junction box and the NTE5 socket had been damaged.

The services to my flat were were refurbished back in March. This included installation of a renewed drop cable and a new IDC junction box. The existing run of cable to the telephone socket (old BT pre-NTE5 pattern) was left as is and merely connected to the junction box. The only other thing done was that the engineer tidied up the cable near the door using a cable tacker gun.

Things were fine for about 3 months and then a strange fault appeared — ADSL service continued (at reduced speed) but the phone went dead. After doing basic checks I called out the BT engineer. He did his thing for a while and then concluded that the connections to the junction box IDC terminals must have been flakey. Instead of reinserting the lines in the IDC connectors, he joined the 2 active lines between drop cable and internal cable using jelly crimp connectors. Apart from that he changed the old BT socket fascia for an NTE5 one.

Once more things ran fine for a couple of months until this week when the system started failing intermittently and then altogether. Being a bit peed off I decided to sort it myself. Using a DMM I found that there was no voltage between the active lines at the phone socket. Cutting off the jelly crimps at the junction box, there was a -50V voltage on the active drop cable lines. This suggested a line break somewhere between junction box and telephone socket. I got hold of some cheapo extension cable from my local Waites and installed that temporarily. Happily, this restored voice/ADSL service (latter at somewhat reduced speed). Hence my desire to replace that with decent quality cable. I think that what happened is that the "tidying up" of the cable using the tacker gun damaged/stretched the existing cable so it became flakey.

As it happens, the cable from the Ebay supplier turned up this morning and this looks to be good stuff, just like Lectrician described. The outer sheath is reasonably firm, the blue/orange pairs are clearly separated with a different rate of twist applied to each pair as it should be. I'll install it this weekend.

Thanks for help given.

Joe

 

[simonpolly]

Is the cable two pr internal cable,blue white fleck,white blue fleck,orange white fleck ,white orange fleck this is what openreach now use,it used to be 3 pr blue,orange,green and before that orange blue,green black .

 

[joegib]

Yup:

1. Mainly Orange with White bands
2. Mainly White with Orange bands

3. Mainly Blue with White Bands
4. Mainly White with Blue bands

Joe

 

[simonpolly]

That will do ,openreach keep changing the colour coding and amount of pairs in the internal wiring,no engineer is going to pick you up if you use this cable,the chance of you getting a fault in the new length of cable is very unlikely and openreach is responsible upto and including the nte.(if you have a staple gun to tack the cable use that,or use white cleats.(how are you going to join it in the bt 78 by the door ?)

 

[Paul_C]

and before that orange blue,green black .

Blue, orange, green, brown.

 

[simonpolly]

and before that orange blue,green black .

Blue, orange, green, brown.

Just checking you were paying attention,you`d think working for openreach i`d know the colour codes ,my mistake must check my posts in future

 

[joegib]

That will do ,openreach keep changing the colour coding and amount of pairs in the internal wiring,no engineer is going to pick you up if you use this cable,the chance of you getting a fault in the new length of cable is very unlikely and openreach is responsible upto and including the nte.(if you have a staple gun to tack the cable use that,or use white cleats.(how are you going to join it in the bt 78 by the door ?)

I used decent quality punchdown tool at the socket and junction box so didn't have any trouble with the IDC connections. For the cable run I used 4mm cable clips though I find it hard to do a neat job with these, especially in corners. There always seem to be slight kinks and curves in new cable that somehow leave traces in the finished job.

Despite my suspicion that use of a tacker gun caused my problem in the first place I was impressed by the neatness of the job they do. I generally remove cable clips when I'm decorating the area involved but restoring them can be a trial.

So, I'm tempted to get one (which I'll use very, very carefully!). Can you recommend any particular brand/model, please? I don't really need 'professional' quality, just something that'll last through a few decoration cycles and for which cable staples are easily obtainable. I have in mind something around £20 though that's flexible.

Thanks

Joe

 

[simonpolly]

If you have damaged the cable in the past its either because the tacs are the wrong size or too much pressures was applied this is what i use,believe me after you`ve tacked 40m of cable and then damage it and have to re do it you soon learn to check the size a pressure first

Untitled

• simonpolly
• 27 Sep 2009
• 1

Tacwise Z3 CT45 Metal Cable Tacker screwfix

 

[joegib]

I'll have a look at that that model. Thanks very much for all your help.

Joe

 

[Paul_C]

Just checking you were paying attention,you`d think working for openreach i`d know the colour codes ,my mistake must check my posts in future

The man who never makes a mistake never does anything. (As I had to tell myself just recently after spending half an hour scratching my head wondering why an ISDN line worked perfectly on the test set but not when connected to the PBX - Turned out I'd swapped the jumpers and had cross-connected Tx and Rx ).

Don't know if you find this, but it's surprising how many now seem to have no idea of the old B/O/G/BN wiring, even though there must be a fair amount still in use out there. I even had quite an argument once with somebody who insisted that the line "couldn't possibly be on blue & orange, because that would be splitting a pair." No amount of explaining seemed to help.

 

[simonpolly]

the days of split pairs are long gone now,PQ and eclipse picks it up everytime,nothing worse than faulting a new line then it coming up unbalanced cable.Working for bt its easy to get confused from time to time.